On both occasions staff were threatened with a blade before the raiders made off with cash.

The first raid happened when two men entered a convenience store in Lowedges Road, Lowedges, on Sunday, September 3, at 9.15pm.

One of them was reported to have threatened staff with a knife before using it to prise the till open. They fled the scene with cash and a quantity of cigarettes.

Two men struck again at the Spar shop in nearby Bocking Lane, Greenhill, at 9.40pm last night.

One of them is reported to have threatened staff with a knife, before prising the till open and taking cash before both fleeing the scene in a silver coloured vehicle.

A spokesperson for Spar said: “"We take this matter very seriously and our priority is the safety of our staff.

"We can confirm that no staff were hurt in the incident and we are continuing to support our colleagues, as well as working with the police as they investigate this case.”

South Yorkshire Police said they believe the incidents are linked and the men in both raids wore dark coloured clothing and had their faces covered.

They are described as being about 5ft 7ins to 6ft tall and of a medium to stocky build.

Detective constable Newman Holt said: "Fortunately there have been no injuries sustained by anyone during the robberies, however those involved are extremely shaken and distressed by the incidents."

"We have visited supermarkets and convenience stores in the local areas, offering support and advice.

"I would encourage stores to please be vigilant and to report any suspicious behaviour to police.

"We do believe the two robberies are linked and we have already conducted a number of enquiries and have various leads to follow up, however I would urge the public to please come forward if they have any information, either by calling 101 or Crimestoppers anonymously on 0800 555111."